Lab tests reveal how asteroids crumble over vastly different timescales

In a laboratory somewhere, researchers have been dropping rocks. Not casually—systematically, repeatedly, in controlled tumbling experiments designed to answer a question that matters far more than it might sound: how long does it actually take an asteroid to fall apart?

The answer, it turns out, is wildly variable. A team of scientists has measured the friability of meteorites—their tendency to crumble under the repeated low stresses of collision and impact—and found that the timescales for complete disaggregation span more than six orders of magnitude. That means some asteroids might shed their surfaces in a geologically brief span, while others could remain largely intact for periods so long they dwarf human comprehension. This discovery fundamentally reshapes how planetary scientists think about asteroid evolution.

The researchers conducted mechanical tumbling experiments on a broad range of stony near-Earth objects, subjecting them to repeated impacts in controlled conditions. What emerged from the data was a pattern: disaggregation does not proceed at a steady rate. Instead, it follows what the team describes as a bounded multiplicative process. Early on, as impacts accumulate, the crumbling accelerates. But then something unexpected happens. As breakable material becomes exhausted, the process slows. The researchers developed a log-logistic model to capture this behavior—a mathematical framework that accounts for a material-dependent limit they call the "pillow-effect."

The pillow-effect is the key to understanding why some asteroids, despite being rubble piles held together by little more than gravity and friction, maintain coherent surfaces. As tumbling and impacts generate fine dust, that dust accumulates in the spaces between larger fragments. Under the microgravity environment of an asteroid, this fine debris acts as a cushion, dampening the energy of subsequent impacts and actually enhancing cohesion. It is a counterintuitive mechanism: the very process of breaking down creates conditions that resist further breaking down.

This finding has direct implications for understanding real asteroids that spacecraft have visited. Bennu and Ryugu, both rubble-pile asteroids explored by recent missions, present a puzzle to scientists: their surfaces appear weak, yet they hold together. The friability measurements suggest an explanation. The fine dust generated from friable materials, accumulating under microgravity, could provide the weak yet cohesive surfaces these asteroids display. The laboratory results offer a physical mechanism for what observations had only hinted at.

The six-order-of-magnitude spread in disaggregation timescales means that regolith maturation—the process by which an asteroid's surface evolves through impact and weathering—and rubble-pile evolution occur over timescales far broader than previously assumed. Some asteroids may mature their surfaces in millions of years; others might require billions. This has cascading consequences for models of asteroid collisional history, for predictions about how asteroid families evolve, and for understanding the long-term stability of small bodies in the inner solar system.

The research provides a quantitative framework that planetary scientists can now incorporate into asteroid evolution models. Rather than relying on rough estimates or assumptions about how quickly different asteroid types break down, researchers have measurements grounded in controlled laboratory conditions. The log-logistic model captures the physics of the process—the acceleration, the plateau, the material-dependent limits—in a form that can be applied across diverse asteroid compositions and sizes. This is the kind of foundational work that transforms a field from qualitative intuition to quantitative prediction.